Control of tension on tape in tape recorders



Oct. 4, 1960 A. L. HERRMANN 2,954,939

CONTROL OF TENSION ON TAPE IN TAPE RECORDERS Filed June 23, 1955 .III I:16 Jl lllllllll? IIIIIIIIIIIIIIIIIIIIII!Illlllllllll Willi INVENTOR.

Adolf L.Herrmann ATTORNEYS United States Patent 2,954,939 CONTROL OFTENSION ON TAPE IN TAPE RECORDERS Adolf. L. Herrmann, Huntsville, Ala.,assignor to the United States of America as represented by theSecretary'of the Army Filed June 23, 1955, Ser. No. 517,671 '4 Claims.(Cl. 242-5512) (Granted under Title 35, US. Code (1952), see. 266) Thisinvention may be manufactured and used by or for the U.S. Governmentwithout the payment to me of any royalties thereon.

This invention relates to a novel arrangement for maintaining.substantially constant tension in a web or filament during winding anduwindi-ng thereof and for maintaining such tension on the web orfilament after stopping, and more particularly to a system. particularlyadapted for use in tape recorders.

It is very important that thetension in the tape of tape recorders be ofthe proper value. If the tension is too high, the tape is apt to tear orslip on the driving sprocket; If there are teeth on. the drivingsprocket, they are apt'to tear through the perforations. On the otherhand-if the tension is not high enough, the tape will tend to. slip onthe driving sprocket. Also, if tension is too low, the tape will winditself loosely on the reels, which willlnot be filled to capacity. In anextreme case, it is possible that. the tape leave its normal pathaltogether.

In the past, one of the most common ways of correcting'this trouble wasto have another motor besides the synchronous motor that drives the tapesprocket. This second motor was connected through friction devices tothe two reels and in this manner tried to keep the tension as the propervalue. In this way, it was necessary that.the torque in. the frictiondevices be high enough when the reels were full and that the speed ofthe motor be high enough when the reels were empty.

This meant that the motor and friction devices had' to. be. designedwith respect to the torque. of the full reel an'd'the speed of the emptyreel. In order that the tape be under tension it. is necessary that thetorque motor run in only one direction. But, since the tape must also berewound, wefind that the friction devices mustnot only account for thechange in speed when the reels are rotating in the same direction, butmust also dissipate the energy brought about when the direction of'.

the reels. is opposite that of the motor. This. always occurs when thereels run from full to empty. Because. of thegreat. losses of power itis necessary that we use alarge motor and of course, the larger themotor, the larger the losses in the motor itself.

Besides this, here is continuous trouble with the, friction devicebecause the friction is always subject to be changed. Therefore,constant checking and adjusting is.

necessary.

To eliminate friction devices, with their troubles, separate tensioningmotors may be used for each reel. But this solution is farfrom beingsatisfactory, because each motor needs to be designed for the speed ofthe empty reeland the torque of the full reel.

. It is therefore an object of my invention to provide a.'novel.tensioncontrol system which will eliminatethe necessity for frictiontype drives and which will maintain substantially constant tensionduring winding and unwinding and while the motor is stopped.

further object is to provide a tension control system whichincorporates. means for differentially driving the take-up and supplyreels and also has a pretensioning- 2,954,939 7 Patented Oct. 4, 1960arrangement and a stop arrangement for pretensioning and. maintainingthe tension in the material in stopped position as well as whilerunning.

Still other objects and many attendant advantages of. my inventionwillbecome apparent to one skilled in the art from a reading of thefollowing detailed descrip tion of an illustrative embodiment thereof,taken in conjunction with the accompanying drawing, wherein Figure 1 isa plan view taken along line 1-1 of Fig. 2 and looking in the directionof the arrows, of a device incorporating my invention- Figure 2 is aview partially in section taken along line 2--2, of Fig. 1 and lookingin the direction of the arrows, embodiment of Figure 1, showing indetail the tape-tensioning mechanism.

This invention eliminates the need of friction devices, and requiresonly one tensioning electromotive (combined motor. and generator) unitof small power.

In the preferred embodiment of my invention the tape and. reels aredriven by a reversible motor and sprocket unit; and on the two reelaxles there are fixed gears that are interconnected through adifferential gearing, the axle of which gearing is rotated by anydifference in the speeds of the reels. To this differential gear axlethere is drivingly connected an electromotive device that acts as atensioning motor when one of the reels is turning faster than a secondreel and as a tensioning generator or braking means when the rotation ofthe reels is reversed and said second reel is turning faster than theabove-mentioned first reel. My optional addition of a light spring motorto this assembly makes it possible to retain the desired tension of thetape for a brief time. when the electromotive unit is disconnected fromits source of electric power, as in a temporary loss of such power.

In Figure l, the tape 3 is equally rolled on reels 1 and 2. The ends ofthe tape are fastened to pins 4 and 5.

The tape is reversibly driven by the unit 6, of known type, whichcomprises a reversible, synchronous electric motor and a sprocket thatis driven by the motor. In the embodiment illustrated, the tape is shownas being driven, by motor-sprocket unit 6-, from reel 1 in the directionof the arrow, over idler reels 7 and past the recording head 8, to reel2. When driven in this direction the tape. will rotate reel 1 but willnot rotate reel 2 unless there is gearing between 1 and 2. Such gearing:is shownin Figure 2 as located on the opposite side of support. 9' fromthe reels and tape that are shown in. Figure 1.

Spur gears 10 and 11, which are rigid with' reels 1 and. 2,respectively, are journaled relative to supporting plate 9, and areconnected by spur and differential gears 12,.

13 and 14. Element 12 is a combined spur and bevel gear, the bevel-gearpart 12A of which engages bevel gear. 13 of the differential gearing.The axle 13A- of bevel gear 13 is welded or otherwise fixed to shaft 15,so that in-ditferential movement gear 13 can revolve around the axis ofshaft 15, as well as rotate on its axle. Shaft 15* is also fixed to spurgear 16, which is in engage ment-withgear. 1-7. The latter gear isdrivingly connected to electromotive device 18, which functions as atensiorv ingsmeansfor'the tape and serves part'of the time as'a motorand part. of the time as a generator.

Electromotive deVice-ll-S-is connected to a power "source throughvariable. resistor 19. With this resistor," itis possible to -changethe: tapeetensioning' torque of said eleetromotive device.

When the motor is'switchedon, torque-is applied through gears-1.7, 16and shaft 15, which transmits torque on. the axle 13Aofgear 13. Gear1-3, which is journaled" on said axle, works on the same principle as ascale bal ance andrtransmits half of the torque to gear IZAand half. ofthe. torque. to gear '14.

Gear 13 will revolve around the axis of shaft and drive gears 12A and 14until all slack is taken up in the tape and the motor stops turning,thereafter holding the tape taut due to its torque.

By changing resistance in the resistor 19 the torque on the motor 18will change, and the tension on the tape can be adjusted. I

When reels '1 and 2 are half filled, that is, when they have the samenumber of turns on each reel, and sprocketand-motor unit 6 is energized,gears 12 and 14 are turned in opposite directions and at the same speed,thereby turning gear 13; but the axle of gear 13 for the moment does notrevolve around the axis of shaft 15.

Thus, for the moment, the electromotive device 18 supplies only torque,without need of its turning, While holding the tape in tensionedposition. In this case, the speed of the reels may be as high aspossible, without power from the motor 18.

With the tape moving from left to right, in the direction of the arrowsof Figure 1, reel 2 will fill and reel 1 will empty, thereby increasingthe speed of reel 1, and decreasing the speed of reel 2, making gear lilrotate faster than gear 11, and gear 12 rotate faster than gear 14. Thedifference between the two speeds will be taken through the axle of gear13, transmitted to shaft 15 and motor 1%, whose torque remains constant.The motor then will turn gear 17 in the direction indicated by the arrownear this gear in Figure 2, thus compensating for the diiference in reelspeeds. In this case the motor thus operates in effect as a drivingmeans, while its torque still holds the tape tensioned. When the tape ismoving from right to left, opposite to the direction of the arrows inFigure 1, reel l'wili fill and reel 2 will empty, thereby decreasing thespeed of reel 1, and increasing the speed of reel 2, making gear 11rotate faster than gear 1th. The difference between the two speeds willbe taken through gear 13, transmitted to shaft 15 and gears 16 and 17and then to device 18. Device 18 then will be forced to turncounterclockwise to compensate for the difierence between the reelspeeds, so that in this case it functions as a generator. Itsfunctioning thus is like the loading and unloading of a coil spring,because at one time the device is taking on power and another time it isgiving off power.

The system just described works only as long as the motor is connectedto the power source, but when the motor 18 is switched off, as by apower failure, tension is immediately lost in the recording tape. Toprovide a means to eliminate this problem, there is provided a spring inthe mechanism between the motor and the reels. This spring may beincorporated into the design between gear 11 and reel 2. It is alsopossible to apply this spring between gear 10 and reel 1, or between themotor and shaft 15. In all cases the effect will be the same; thereforetwo or three springs could be used, if necessary, for greater capacity.In the mechanism shown (Figure 2) the spring 20 is applied between gear11 and reel 2. This spring initially will absorb the energy of severalrevolutions of the motor 18 and store this energy until the torque in itis equal to that developed by the motor; The spring 20 thus is able toact as an elastic coupling between gear 11 and reel 2 and will turnclockwise or counterclockwise with reel 2.

' When the motor 18 is turned on, spring 20 immediately will load untilthe torque on thespring is equal to the torque being applied by themotor. Therefore, the tape immediately will acquire the necessarytension. Thereafter, the system works as described in previousparagraphs. I p

If after recording, or accidentally during operation of the tape, supplyof current to the motor ceases, the spring immediately tries to unloadits tension; this is prevented on one side by the tape being connectedto the two reels. The tendency of the spring to unload on the otherside, through the motor, is preventedby a spring-and-solenoid brake 2:1,22 which is applied to gear 16 and is in the same circuit with themotor. The brake is held against the gear by the spring 22 until themotor is again turned. V on, and current energizes the solenoidcompressingspring 22 against spring seat 23, thus withdrawing the brake.The brake can be applied as shown, or it can be applied on the motorshaft, or the brake and the motor can be combined into one unit.

It will be readily apparent that many modifications may be made withoutdeparting from the scope of the invention. Therefore it is to beunderstood that the scope of the invention is restricted only asdescribed in the appended claims. I

I claim I 1. A reeling mechanism, for winding and unwinding a I flexibleelement comprisingzan elongated support; a pair of laterally spacedbearings onsaid support; a third bear ing on'said supportbetweensaidpair of bearings; a pair of shafts journalled in'said pair ofbearings, each of said shafts extending a substantial distance oneachside of said support; a pair of reels fixedto said shafts on one side ofsaid support; means for attaching the ends of said flexible element tosaid reels; means connected to said flexible "element for driving saidelement; a first reel-coaxial gear, parallel with and adjacent saidsupport,

' fixed to one of said shafts on the side of. said support op-.,

posite from said reels; a second reel-coaxial gear, parallel with saidsupport, and spaced from the support farther than saidfirst reelcoaxialgear; means operatively connecting said second reel-coaxial gear to theother one of said pair of shafts; a third shaft, journalled at one ofits ends in said third bearing, extending a substantial distancefrom-the side of said support that is opposite from said reels; a firstdifferential gear, journalled on said third shaft, adjacent saidsupport, and in meshwith said first reel-coaxial gear; a seconddifferential gear, fixed to said third shaft and in mesh with saidsecond reelcoaxial gear; an axle fixed to and normal to said thirdshaft; a third differential gear journalled on said axle and in meshwith said first and second differential gears; an electromotivetorque-supplying device; means for supplying electric current tosaidelectromotive device; and reduction gearing for transmitting torquebetween said electromotive device and an end of said third shaft.

2. A device as set forth in claim 1, in which said reduction gearing isdrivingly connected to the end of said third shaft that is farthest fromsaid third bearing.

3. A device as set forth in claim 1, in which said means operativelyconnecting said second reel-coaxial gear to said other one ofsaid pairof shafts comprises a spring motor that stores energy whencurrent isbeing supplied 9 to said electromotive device, and that rotates saidreels References Cited in the file of this patent UNITED STATES PATENTS1,996,815 Kimpton et are; Apr. 9, 1935 2,034,543 'Iwiss et al. Mar. 17,1936 2,389,047 Heinz -1 Nov. 13, 1945 2,517,055 Thompson Aug. 1, 19502,626,760 Chick 'Jan. 27, 1953 2,632,060 Foote et a1 Mar. 17, 1953FOREIGN PATENTS 1,067,954 France Feb. 3, 1954 Warn

